Soil contamination, such as by industrial activity and agricultural chemicals, is a serious concern throughout the world. The contamination may be a result of spills, accidents, or improper disposal of waste. The problem of soil contaminated by organic pollutants such as hydrocarbons, polynuclear aromatics, organo-chlorinated products is becoming increasingly more dramatic in industrialized countries, not only in terms of interventions on pollution of soil and underground water, but the necessity to use contaminated lands for industrial and civil use. There are many sources of pollution and various characteristics of soil subjected to contaminants. Contaminants in the soil can adversely impact the health of animals and humans when they ingest, inhale, or touch contaminated soil, or when they eat plants or animals that have uptaken contaminants from soil. Animals ingest and come into contact with contaminants when they burrow in contaminated soil. For example, many of the widely used pesticides on agricultural lands are potentially carcinogenic. The U.S. Environmental Protection Agency (EPA) identified 15 such chemicals from the 27 most commonly used. Remediation methods include ex situ methods such as excavation of affected soils and subsequent treatment at the surface, and in situ methods which treat the contamination without removing the soil.
Prior to determining the appropriate remediation, the contamination site must be identified, including delineating the extent of the contamination of both soil and groundwater, as the effectiveness of the in situ chemical oxidation technology is site specific. Further, the contaminants, and the characteristics of the contaminants, must be identified, including amounts and concentrations. Based on the contamination, the geology, hydrology and hydrogeology are determined. The injection of oxidants into the groundwater may cause contamination to spread faster than normal, depending on the contaminant and the site's hydrogeology. For example, some metal contaminants increase solubility in an oxidizing environment or reducing environment, thereby increasing contamination migration rates. Once the site analysis is complete, a remedial action plan may be determined.
Solidification and stabilization technology that relies on the reaction between a binder and soil to stop/prevent or reduce the mobility of contaminants. For example, a reactive wall is assembled for remediation of contaminated underground water using granular iron has been in use as reactive medium. In one variation, a mixture of iron and ferrous sulfide is used to remediate soils of halogenated hydrocarbons. In another, a tiered iron wall or column, comprising in at least three zones of graduated sizes of iron particles as reactive medium is used for halogenated hydrocarbons. Iron (Fe°) undergoes oxidation, forming redox couples thereby de-halogenating and oxidizing the contaminants. Another variation uses Portland cement or other hydraulic ligand to bind the contaminants in location and physically block the contaminant inside the cementitious matrix preventing further migration of the contaminant into the surrounding environment. The technology has a good success record but suffers from deficiencies related to durability of solutions and potential long-term effects. In addition CO2 emissions due to the use of cement are also becoming a major obstacle to its widespread use in solidification/stabilization.
Excavation or dredging is used to remove contaminated soil, and may also be used to aerate the soil to remove volatile organic compounds (VOCs). Bio-remediation, through bioaugmentation and biostimulation of the excavated material, has shown promise for remediation of semi-volatile organic compounds (SVOCs). Chemical oxidation has also been utilized in the remediation of contaminated soil. This process involves the excavation of the contaminated area into large bermed areas where they are treated using chemical oxidation methods. However, biological remediation is limited to biodegradable compounds and compounds at non-toxic concentrations; in addition the long period of time needed to complete remediation adversely affects the biological systems, limiting use of the technology.
Solubilization and recovery, or surfactant enhanced aquifer remediation, injects hydrocarbon mitigation agents or surfactants into the soil to speed desorption and recovery of bound up contaminants, such as hydrocarbons. Some variations of solubilization and recovery use pollutants' affinity, either chemically or physically, to bind finer particles of the sediment. These particles can be separated from the remaining soil using differential separation techniques through size, density and surface properties. The separated, fine particles are a small fraction of soil, but contain the majority of pollutants. However, this process requires large volumes of surfactant and also possesses difficulty in recovering the surfactants.
In situ organic pollutants removal includes extraction, such as using lipophylic solvent and treating the purified soil with water to remove the residual solvent (D'Angeli, et al., PCT/EP2002/007495). In situ bioremediation has also been used by boring injection holes in the contaminated soil and set casing into the hole to receive the treatment biological materials. This remediation is expensive, cumbersome, requires large equipment, and does not provide a fine adjustment of the remediation process because it relies upon a few large holes and not many small ones to tightly control the treatment area. High pressure gas and oxygen have been added to the hole to drive the biological materials out into the surrounding soil to effect treatment. In some cases this approach uses high pressure and large volumes which have caused contaminants to migrate to previously uncontaminated areas.
In situ oxidation involves the injection of strong oxidants, such as hydrogen peroxide, ozone gas, potassium permanganate or persulfates, into the soil. Each type of oxidant is effective for a different group of contaminants. Among these three oxidants, hydrogen peroxide and ozone are the common selections used to treat petroleum hydrocarbons, benzene, toluene, ethyl-benzene and total xylenes (BTEX) impacted soil and groundwater. Permanganate is believed to have limited effectiveness for BTEX, especially for benzene. The success of in situ chemical oxidation is dependent on effectively delivering chemical oxidants to the contaminant. Upon contact with organic contamination the chemical oxidants will convert them to carbon dioxide, and water in the case of hydrocarbons.
Injection success is a function of pressure and time and time often constitutes difficulty. Traditional injection is laborious, difficult and often the difficulty leads to injection problems like short circuiting to the surface (day lighting) or lack of confidence in injectate placement, which are addressed by the present invention.